The present invention relates to structures, lithographic mask forming solutions, mask forming methods, field emission display emitter mask forming methods, and methods of forming plural field emission display emitters.
Field emission displays are utilized in a variety of display applications. Conventional field emission displays include a cathode plate having a series of emitter tips fabricated thereon. The tips are configured to emit electrons toward a phosphor screen to produce an image. The emitters or emitter tips are typically formed from an emitter material such as conductive polysilicon, molybdenum, or aluminum. Multiple emitters are typically utilized to excite a single pixel. For example, 120 emitters may be used for a single pixel. Individual pixels contain a deposited one of red, green, or blue phosphor.
One method of fabrication of emitter tips is described in U.S. Pat. No. 5,391,259 (the ""259 patent); assigned to the assignee hereof and incorporated by reference. A hardmask layer is formed over emitter material in the disclosed fabrication method. Portions of the hardmask layer are selectively removed to form a hardmask utilized for emitter fabrication. One conventional method utilizes photolithography and etching to selectively remove portions of the hardmask layer. Following the formation of the hardmask, the emitter material is etched isotropically to form the tips. For proper fabrication, it is highly desired that hardmasks be patterned to a consistent critical dimension. Variations in critical dimensions or size of the hardmasks can result in non-uniformity within the formed emitter tips.
One method for fabricating the hardmask utilized to form the emitter tips uses spheres or beads as the mask for creating the hardmask layer mask. The spheres are provided in a liquid medium such as water. The emitter substrate is dipped into a vat of solution containing the spheres. The substrate is then withdrawn from the solution and some of the spheres adhere to the emitter substrate.
It is preferred to achieve a homogeneous/uniform distribution of beads upon the face of the emitter material. However, homogeneous distribution has been difficult to achieve. A non-uniform distribution of beads can result in adjacent spheres touching and subsequent adjoining of emitter tips following emitter fabrication causing problems with electron optics (e.g., focusing of electrons). Such joining of emitter tips can result in the emission of electrons which strike adjacent phosphor patches resulting in poor color intensity and poor color distribution.
Further, the spheres may exhibit poor adhesion to the surface of the substrate when conventional methods of applying the spheres to the substrate surface are utilized. This drawback is particularly acute if the spheres are larger than 0.5 microns.
The present invention provides improvements in device fabrication while avoiding problems experienced in the prior art.
The present invention includes structures, lithographic mask forming solutions, and mask forming methods. The invention further includes field emission display emitter mask forming methods and methods of forming plural field emission display emitters.
One aspect of the present invention provides a lithographic mask forming solution. The solution includes a photosensitive material and a plurality of masking particles within the photosensitive material. The photosensitive material comprises photoresist and the masking particles comprise beads or spheres in exemplary embodiments. The photosensitive material is cured and portions of the cured photosensitive material are removed in preferred aspects of the invention. Masking particles remaining upon the substrate are thereafter used as a mask to process a substrate. Uncured photosensitive material is used to improve adhesion of masking particles to the substrate to be processed.
A second aspect of the invention provides a structure forming method including providing a solution comprising a photosensitive material and a plurality of masking particles. The method also provides applying the solution over a substrate and removing at least a portion of the photosensitive material while leaving the masking particles over the substrate. The solution is preferably screen printed. The method also includes processing the substrate using the masking particles as a mask.
According to another aspect, a method of forming a mask over a substrate includes forming a masking layer over a surface of a substrate. Masking particles are screen printed over a surface of the masking layer and portions of the masking layer are removed using the masking particles. The removing of portions of the masking layer forms a mask. This mask includes a plurality of circular masking elements in some embodiments.
In another aspect, masking particles are mixed within photoresist to form a solution which can be screen printed. The screen printing includes printing masking particles within the solution containing photoresist. In one embodiment, the solution has a concentration within the approximate range of approximately 1xc3x97108-1xc3x97109 masking particles per milliliter of photoresist.
It is preferred to provide a uniform layer of masking particles upon the masking layer. To this end, screen printing of masking particles guides the masking particles to predefined regions over the substrate. Further, the masking particles are preferably agitated to space the masking particles from one another.
In some aspects of the invention, the solution is permitted to cure and portions of the photoresist or other photosensitive material is removed. The masking particles form a mask utilized to form a hardmask from the masking layer. The hardmask is subsequently utilized to form a random array of emitters of a field emission display from an emitter substrate.